Fans of Mary Shelley's Frankenstein recall that the novel came out of a kind of parlor game, three people sitting around and deciding to write competing ghost stories. Well, The Vampyre was one of the other stories. And there's a reason you've probably never heard of it - it's not very good. I believe its primary claim to fame, aside from its origins, is that it is one of the first vampire novels? In any case - it certainly ain't one of the better ones.
Spoilers ahead, FYI.
I suppose part of what makes it intriguing is how sparse it is. There is only one scene of actual vampiricism, and it's thwarted. After that, though the reader is of course like omg duh that dude is a vampire, the evidence is, curiously enough, a weapon left at the scene of the crime - an odd move, when you think about it, given that a vampire is theoretically a walking weapon. What is also curious is that even in this early text, there is already the trope of the main character who has read so many supernatural texts that his judgment is not to be trusted because he's probably imagining things.
The novel does feature some good old eastern exoticism, but then has a return to England (just like Dracula!), where the plot gets pretty ridiculously convoluted, and then ends in a pretty absurdly hasty way.
Not a must read.